Resin-metal laminates

ABSTRACT

A resin composition for coating a metal sheet comprising a polyester resin (A) having an intrinsic viscosity of 0.5-2.0 dl/g, an elastomer resin (B) and a vinyl polymer (C) containing at least 1 wt % of a unit with a polar group, and having a structure wherein the elastomer resin (B) is finely dispersed in the polyester resin (A) and at least a portion of the elastomer resin (B) is capsulated by the vinyl polymer (C). Also, metal-sheet-coating resin films using the resin composition, resin-coated metal sheets coated with the resin film, and resin-coated metal containers made by molding the resin-coated metal sheets are disclosed.

TECHNICAL FIELD

The present invention relates to a resin composition for coating a metalsheet with excellent impact strength, chemical resistance, moldability,heat resistance and gas barrier properties, and satisfactory adhesion tometals. The invention further relates to a resin film for coating ametal sheet employing the resin composition, to a resin-coated metalsheet prepared by coating the resin film onto one or both sides of ametal sheet by single layer or multilayer lamination, and to aresin-coated metal container made by molding the resin-coated metalsheet.

BACKGROUND ART

Polyester resins are widely used as coating materials for metal sheetsfor the purpose of corrosion inhibition, because of their excellentmechanical properties, electrical properties, heat resistance, gasbarrier properties and adhesion with metals.

However, since the metal adhesion, impact strength and gas barrierproperties of a polyester resin are strongly dependent on its degree ofcrystallization, the desired properties cannot be achieved withoutstrict control of the crystal structure inside the coating.Specifically, it is necessary to reduce the crystallization degree atthe resin interface that contacts the metal in order to achieve goodadhesion, while increasing the crystallization at the other sections inorder to ensure impact strength and gas barrier properties; it hastherefore been necessary to provide a suitable gradient ofcrystallization inside the coating that can simultaneously satisfy theadhesion, impact strength and gas barrier properties. AS a result, theconditions for the lamination step have been severely restricted.

As one means of overcoming these disadvantages of polyester resins,Japanese Unexamined Patent Publication HEI No. 3-269074 has disclosed amethod of laminating a resin composition comprising a crystallinepolyester resin and an amorphous polyester resin. While this methodallows improved adhesion since the degree of crystallization can beeasily lowered at the interface during the lamination step, it alsoreduces the gas barrier properties and impact strength, and theexpression of both properties has required restrictions in the steps,such as using a biaxially stretched film to actively retaincrystallization.

Also, Japanese Unexamined Patent Publication HEI No. 7-195617 disclosesa technique for lamination of a metal sheet with a coating comprising acomposition that contains a polyester resin and an ionomer resin. Sincethis technique can maintain impact strength even with a lower degree ofcrystallization, it can provide both adhesion and impact strength;however, it has not been able to achieve sufficient improvement inimpact strength at low temperatures.

Furthermore, Japanese Unexamined Patent Publication HEI No. 7-290643 andJapanese Unexamined Patent Publication HEI No, 7-290644 disclosetechniques wherein a three-component composition of a polyester resin,ionomer resin and polyester elastomer is used as the coating for a metalsheet. These techniques, however, while providing some improvement inimpact strength at low temperatures and impact strength at roomtemperature, have not allowed improvement to a sufficient level.

In Japanese Unexamined Patent Publication SHO No. 58-17148 there isdisclosed a polyester composition containing an aromatic polyester witha specific glycidyl group-containing copolymer and a specific ethyleniccopolymer. However, this patent does not disclose or suggest a resincoating structure, forming the basis of the present invention, wherebyan elastomer resin capsulated by a polar group-containing resin isdispersed in a polyester resin. Moreover, the composition disclosed inthis patent is a resin composition used to obtain molds by injectionmolding or extrusion molding, and therefore differs substantially fromthe metal sheet coating resin film of the present invention in terms ofits purpose of use.

It is therefore an object of the present invention to provide a resincomposition for coating a metal sheet that exhibits not only excellentimpact strength, chemical resistance, moldability, heat resistance andgas barrier properties, but also excellent adhesion with metals.

It is another object of the invention to provide a resin film forcoating a metal sheet employing the resin composition, to provide aresin-coated metal sheet coated with a resin coating of the laminatedresin film, and to provide a resin-coated metal container formed bymolding the resin-coated metal sheet.

DISCLOSURE OF THE INVENTION

Specifically, the invention relates to a resin composition for coating ametal sheet characterized by comprising a polyester resin (A) having anintrinsic viscosity of 0.5-2.0 dl/g, an elastomer resin (B) and a vinylpolymer (C) containing at least 1 wt % of a unit with a polar group, andhaving a structure wherein the elastomer resin (B) Yes finely dispersedin the polyester resin (A) and at least a portion of the elastomer resin(B) is capsulated by the vinyl polymer (C); it further relates to aresin composition for coating a metal sheet comprising 1-50 parts byweight of an elastomer resin (B) and 1-50 parts by weight of a vinylpolymer (C) with respect to 100 parts by weight of a polyester resin(A), wherein the sphere equivalent diameter of the elastomer resin (B)finely dispersed in the polyester resin (A) is no greater than 1 μm.

The invention still further relates to a resin composition for coating ametal sheet wherein the polyester resin (A) is composed of an acidcomponent comprising 50-95 mole percent of terephthalic acid and 50-5mole percent of isophthalic acid and/or orthophthalic acid, and a diolcomponent comprising a glycol of 2-5 carbon atoms. It still furtherrelates to a resin composition for coating a metal sheet wherein theelastomer resin (B) is a polyolefin resin, and the polyolefin resin is acopolymer of ethylene and an α-olefin of 3 or more carbon atoms, or aterpolymer comprising ethylene, an α-olefin of 3 or more carbon atomsand a non-conjugated diene. It still further relates to a resincomposition for coating a metal sheet wherein the vinyl polymer (c) isan ionomer resin.

The invention further relates to a resin composition for coating a metalsheet wherein the elastomer resin (B) and vinyl polymer (C) form acore-shell type elastomer, x,ith the elastomer resin (B) as the core andthe vinyl polymer (C) as the shell; it still further relates to a resincomposition for coating a metal sheet wherein the vinyl polymer (C) isan acrylate-based polymer, and units containing epoxy groups or aromaticpolyester bonds are introduced into the acrylate-based polymer at nogreater than 15 wt % with respect to the acrylate units.

The present invention further relates to a resin film for coating ametal sheet formed by laminating the aforementioned resin composition,either alone or in combination with another resin composition and/oradhesive, it even still further relates to a resin-coated metal sheetobtained by coating the metal-sheet-coating resin film onto one or bothsides of a metal sheet in a single layer or multilayer form, and it yetstill further relates to a resin-coated metal container made by moldingthe resin-coated metal sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 are illustrations of resin-coated metal sheets according tothe invention. FIG. 1 shows a case with a single layer laminated on oneside and FIG. 2 a case with a single layer laminated on both sides,where 1 is the metal sheet, and 2 and 3 are resin films of theinvention. In FIG. 3, 1 is the metal sheet, 2 s a multilayer resin filmand 2-1 to 2-3 are the respective resin films forming the multilayerfilm; one or more of the resin films 2-1 to 2-3 may be resin filmsaccording to the invention, and 3 is a resin film on the opposite side;the resin film 3 may be a resin film according to the invention or adifferent type of resin film.

FIG. 4 shows a container molded by drawing using a resin-film-coatedmetal sheet such as shown in FIG. 2. Here, 1 is the metal sheet and 2and 3 are resin films.

BEST MODE FOR CARRYING OUT THE INVENTION

The resin composition for coating a metal sheet, the resin filmemploying it, the resin-coated metal sheet and the resin-coated metalcontainer according to the invention will now be explained.

The resin composition for coating a metal sheet of the inventioncomprises a polyester resin (A) having an intrinsic viscosity of 0.5-2.0dl/g, an elastomer resin (B) and a vinyl polymer (C) containing at least1 wt % of a unit with a polar group, and it must have a structurewherein the elastomer resin (B) is finely dispersed in the polyesterresin (A) and at least a portion of the elastomer resin (B) iscapsulated by the vinyl polymer (C).

Here, “finely dispersed” is a condition in which the elastomer resin (B)is dispersed in the polyester resin (A) at a sphere equivalent diameterof no greater than 100 μm. If the sphere equivalent diameter of theelastomer resin (B) exceeds 100 μm, it becomes difficult to work theresin composition of the invention into a film. The sphere equivalentdiameter is preferably no greater than 1 μm, and more preferably nogreater than 0.5 μm. At greater than 1 μm, it is sometimes not possibleto exhibit sufficient impact strength.

The elastomer resin (B) being capsulated by the vinyl polymer (C) is astructure wherein at least 80%, and preferably at least 95%, of theinterface of the elastomer resin (B) is covered by the vinyl polymer(C), and the area of direct contact between the polyester resin (A) andthe elastomer resin (B) is less than 20%. With this type of structure,the vinyl polymer (C) provides adhesion with the metal sheet even if theelastomer resin (B) contacts the metal sheet, and therefore adhesionbetween the resin composition and the metal sheet can be guaranteed.

It is not necessary for the entirety of the elastomer resin (B) to becapsulated by the vinyl polymer (C), and it is sufficient if at least70% of the volume of the elastomer resin (B) is capsulated by the vinylpolymer (C). When greater than 30% of the volume of the elastomer resin(B) is not capsulated, the proportion of the elastomer resin (B) indirect contact with the metal sheet will increase when the resincomposition is used to coat the metal sheet, and therefore it will nolonger be possible to guarantee adhesion between the resin compositionand the metal sheet. The sphere equivalent diameter of thenon-capsulated elastomer resin (B) is not particularly restricted, butfrom the standpoint of impact strength and workability, it is preferablyno greater than 0.5 μm.

The excess vinyl polymer (C) that does not capsulate the elastomer resin(B) may be dispersed alone in the polyester resin (A). The amount andsize of the non-capsulating vinyl polymer (C) is not particularlyrestricted, but it is preferably no more than 20% in terms of volumeratio to the total vinyl polymer (C), with a sphere equivalent diameterof no greater than 0.5 μm. With a volume ratio of greater than 20%, thefundamental properties such as the heat resistance of the resincomposition can sometimes be altered. With a sphere equivalent diameterof greater than 0.5 μm, the workability is sometimes lowered.

The resin composition for coating a metal sheet of the invention mayhave the structure described above and its composition is not otherwiserestricted, but it is preferably a resin composition for coating a metalsheet comprising 1-50 parts by weight of an elastomer resin (B) and 1-50parts by weight of a vinyl polymer (C) with respect to 100 parts byweight of a polyester resin (A). If the elastomer resin (B) is presentat less than 1 part by weight it may not be possible to impartsufficient impact strength, and if it is present at greater than 50parts by weight the heat resistance may be reduced. If the vinyl polymer(C) is present at less than 1 part by weight it may not be able toadequately capsulate the elastomer resin (B), and if it is present atgreater than 50 parts by weight the heat resistance may be reduced.

The polyester resin (A) used for the invention has an intrinsicviscosity of 0.5-2.0 dl/g, preferably 0.65-1.7 dl/g, and more preferably0.8-1.5 dl/g. If the intrinsic viscosity is less than 0.5 dl/g it willnot uniformly mix with the elastomer resin (B) and the polarmonomer-containing vinyl polymer (C), thus leading to lower mechanicalstrength and impact strength, while if the intrinsic viscosity isgreater than 2.0 dl/g the moldability will be poor, and thus neithersituation is desirable.

The intrinsic viscosity is determined by measurement according to thefollowing formula (i) at a 0.5% concentration in o-chlorophenol at 25°C. In the formula, C represents the concentration in terms of number ofgrams of resin per 100 ml of solution, t₀ represents the flow time ofthe solvent, and t represents the flow time of the solution.

Intrinsic viscosity={1n(t/t ₀)}/C  (i)

The polyester resin (A) used for the invention is a thermoplasticpolyester having as the structural unit only a hydroxycarboxylic acidcompound residue, or a dicarboxylic acid residue and a diol compoundresidue, or a hydroxycarboxylic acid compound residue and a dicarboxylicacid residue and diol compound residue. Mixtures of these are alsoincluded.

As examples of hydroxycarboxylic acid compounds to be used as startingmaterials for hydroxycarboxylic acid compound residues there may bementioned p-hydroxybenzoic acid, p-hydroxyethylbenzoic acid and2-(4-hydroxyphenyl)-2-(4′-carboxyphenyl)propane, and these may be usedalone or in mixtures of two or more.

As examples of dicarboxylic acid compounds that form dicarboxylic acidresidues there may be mentioned aromatic dicarboxylic acids such asterephthalic acid, isophthalic acid, orthophthalic acid,1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid,2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid,diphenic acid, diphenyldicarboxylic acid and diphenoxyethanedicarboxylicacid; aliphatic dicarboxylic acids such as adipic acid, pimelic acid,sebacic acid, azelaic acid, decanedicarboxylic acid, malonic acid,succinic acid, malic acid and citric acid; and alicyclic dicarboxylicacids such as cyclohexanedicarboxylic acid, any two or more of which maybe used in admixture.

As examples of diol compounds that form diol residues there may bementioned aromatic diols such as 2,2′-bis(4-hydroxyphenyl)propane(hereunder abbreviated to “bisphenol A”), bis(4-hydroxyphenyl)methane,bis(2-hydroxyphenyl)methane, o-hydroxyphenyl-p-hydroxyphenylmethane,bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone,bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone,bis(4-hydroxyphenyl)ketone, bis(4-hydroxyphenyl)diphenylmethane,bis(4-hydroxyphenyl)-p-diisopropylbenzene,bis(3,5-dimethyl-4-hydroxyphenyl)methane,bis(3-methyl-4-hydroxyphenyl)methane,bis(3,5-dimethyl-4-hydroxyphenyl)ether,bis(3,5-dimethyl-4-hydroxyphenyl)sulfone,bis(3,5-dimethyl-4-hydroxyphenyl)sulfide,1,1-bis(4-hydroxyphenyl)ethane,1,1-bis(3,5-dimethyl-4-hydroxyphenyl)ethane,1,1-bis(4-hydroxyphenyl)cyclohexane,1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,1,1-bis(4-hydroxyphenyl)-1-phenylethane,1,1-bis(4-hydroxyphenyl)-1-phenylmethane,2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)butane,2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane,2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane,2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane,2,2-bis(3-methyl-4-hydroxyphenyl)propane,2,2-bis(3-chloro-4-hydroxyphenyl)propane,2,2-bis(3-bromo-4-hydroxyphenyl)propane,1,1,1,3,3,3-hexafluoro-2,2-bis(4-hydroxyphenyl)propane,4,4′-biphenol,3,3′,5,5′-tetramethyl-4,4′-dihydroxybiphenyl and 4,4 ′dihydroxybenzophenone; aliphatic diols such as ethyleneglycol,trimethyleneglycol, propyleneglycol, tetramethyleneglycol,1,4-butanediol, pentamethyleneglycol, neopentylglycol,hexamethyleneglycol, dodecamethyleneglycol, diethyleneglycol,triethyleneglycol, tetraethyleneglycol, polyethyleneglycol andhydrobisphenol A; and alicyclic diols such as cyclohexanedimethanol;these may be used alone or in mixtures of two or more. Polyester resinsobtained therefrom may also be used alone or in mixtures of two or more.

The polyester resin (A) used for the invention may be composed of theseresidues or combinations thereof, but preferred among them from thestandpoint of workability and thermal stability are aromatic polyesterresins composed of aromatic dicarboxylic acid residues and diolresidues.

The polyester resin (A) used for the invention may also contain aconstituent unit derived from a polyfunctional compound such as trimesicacid, pyromellitic acid, trimethylolethane, trimethylolpropane,trimethylolmethane and pentaerythritol in a small amount, for example inan amount no greater than 2 mole percent.

From the standpoint of heat resistance and workability, the mostpreferred combination among combinations of these dicarboxylic acidcompounds and diol compounds are compounds comprising dicarboxylic acidcompounds with 50-95 mole percent terephthalic acid and 50-5 molepercent isophthalic acid and/or orthophthalic acid, and diol compoundsof glycols with 2-5 carbon atoms.

As preferred examples of the polyester resin (A) used for the inventionthere may be mentioned polyethylene terephthalate, polybutyleneterephthalate, polyhexamethylene terephthalate,polycyclohexylenedimethylene terephthalate, polyethylene-2,6-naphthalateand polybutylene-2,6-naphthalate, among which the most preferred arepolyethylene terephthalate, polybutylene terephthalate,polyethylene-2,6-naphthalate and polybutylene-2,6-naphthalate because oftheir suitable mechanical properties, gas barrier properties and metaladhesion.

The polyester resin (A) used for the invention preferably has a glasstransition temperature (Tg, measured by a differential scanningcalorimeter (DSC) with an approximately 10 mg sample and a temperatureelevating rate of 10° C./min) of 50-120° C., and more preferably 60-100°C. The polyester resin (A) may be amorphous or crystalline, and whencrystalline the crystal melting temperature (Tm) is usually 210-265° C.and preferably 210-245° C., while the low crystallization temperature(TC) is usually 110-220° C. and preferably 120-215° C. If the Tm isbelow 210° C. or the Tc is below 110° C., the heat resistance may beinsufficient and the film shape may not be retainable during drawworking. If the Tm is above 265° C. or the Tc is above 220° C., theresin may not adequately fill in the surface irregularities of the metalsheet, leading to poor adhesion.

The elastomer resin (B) used for the invention may generally be anypublicly known elastomer resin. Preferred are elastomer resins whereinthe glass transition temperature (Tg, measured by a differentialscanning calorimeter (DSC) with an approximately 10 mg sample and atemperature elevating rate of 10° C./min) of the elastomeric portion isno higher than 50° C., the Young's modulus at room temperature is nogreater than 1000 MPa and the elongation at break is at least 50%. Ifthe Tg of the elastomeric portion is above 50° C., the Young's modulusat room temperature is above 1000 MPa or the elongation at break is lessthan 50%, it may not be possible to exhibit sufficient impact strength.In order to ensure impact strength at low temperatures, it is preferredfor the Tg to be no higher than 10° C., and more preferably no higherthan −30° C. To ensure more reliable impact strength, the Young'smodulus at room temperature is preferably no greater than 100 MPa andmore preferably no greater than 10 MPa, and the elongation at break ispreferably at least 100%, and more preferably at least 300%.

As specific examples of the elastomer resin (B) used for the inventionthere may be mentioned polyolefin resins; diene elastomers such asstyrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer(NBR), polyisoprene (IPR) and polybutadiene (BR); styrene-basedelastomers such as styrene-butadiene-styrene copolymer (SBS) and itshydrogenated form (SEBS), rubber-modified styrene (HIPS) andacrylonitrile-styrene-butadiene copolymer (ABS); silicon elastomerscomposed mainly of dimethylsiloxane; polyester elastomers such asaromatic polyester-aliphatic polyester copolymers or aromaticpolyester-polyether copolymers; nylon elastomers, and the like.

Among these, polyolefin resins are preferred because of their low watervapor permeability. Polyolefin resins are resins with a repeating unitrepresented by the following general formula (a):

—R₁CH—CR₂R₃—  (a)

where R₁ and R₃ each independently represent an alkyl group of 1-12carbon atoms or hydrogen, and R₂ represents an alkyl group of 1-12carbon atoms, a phenyl group or hydrogen.

The polyolefin resin used for the invention may be a simple polymer ofone such structural unit, or a copolymer of two or more different types,and it may also be a copolymer of resin units formed of such units.

As examples of such repeating units there may be mentioned aliphaticolefins of repeating units that appear with addition polymerization ofo-olefins such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene,1-hexene, 1-octene, 1-decene and 1-dodecene, or repeating units fromaddition of isobutene, and aromatic olefins of addition polymer unitssuch as styrene monomers, as well as alkylated styrenes such as o-, m-,p-methylstyrene, o-, m-, p-ethylstyrene or t-butylstyrene, halogenatedstyrenes such as monochlorstyrene, and styrene-based monomers such asα-methylstyrene.

As examples of polyolefin resins there may be mentioned polyethylene,polypropylene, polybutene, polypentene, polyhexene and polyoctenylene,as simple α-olefin polymers. Copolymers of the aforementioned copolymersinclude aliphatic polyolefins such as ethylene-propylene copolymer,ethylene-butene copolymer, ethylene-propylene-1,6-hexadiene copolymer orethylene-propylene-5-ethylidene-2-norbornene copolymer, and aromaticpolyolefins such as styrene-based polymers; however, there is nolimitation to these, and it is sufficient to satisfy the description ofthe repeating units given above. These resins may be used alone or inmixtures of two or more.

The polyolefin resin may have one of the aforementioned olefin units asits main component, and it may be copolymerized with a vinyl monomer,polar vinyl monomer or diene monomer copolymerized as a monomer unit orresin unit substituting the aforementioned units. A copolymerizingcomponent may be used at no more than 50 mole percent, and preferably nomore than 30 mole percent, with respect to the aforementioned units. Atgreater than 50 mole percent, the properties of the polyolefin resin,such as dimensional stability, may be reduced.

As examples of polar vinyl monomers there may be mentioned acrylic acidderivatives such as acrylic acid, methyl acrylate and ethyl acrylate,methacrylic acid derivatives such as methacrylic acid, methylmethacrylate and ethyl methacrylate, acrylonitrile, maleic anhydride,imide derivatives of maleic anhydride, vinyl chloride, and the like.

As diene monomers there may be mentioned butadiene, isoprene,5-methylidene-2-norbornane, 5-ethylidene-2-norbornane, dicyclopentadieneand 1,4-hexadiene.

The most preferred resins as polyolefin resins for imparting impactstrength are copolymers of ethylene and α-olefins of 3 or more carbonatoms, such as ethylene-propylene copolymer, ethylene-butene-1copolymer, ethylene-pentene-1 copolymer, ethylene-3-ethylpentenecopolymer and ethylene-octacene-1 copolymer; or terpolymers comprisingethylene, an α-olefin of 3 or more carbon atoms and a non-conjugateddiene, obtained by copolymerizing butadiene, isoprene,5-methylidene-2-norbornane, 5-ethylidene-2-norbornane, dicyclopentadieneor 1,4-hexadiene with the aforementioned binary polymers. For their easeof handling, it is preferred to use binary copolymers such asethylene-propylene copolymer and ethylene-butene-1 copolymer, or resinsobtained by copolymerizing 5-methylidene-2-norbornane,5-ethylidene-2-norbornane, dicyclopentadiene or 1,4-hexadiene asnon-conjugated dienes with ethylene-propylene copolymer orethylene-butene-1 copolymer, with the α-olefin at 20-60 mole percent andthe non-conjugated diene at 0.5-10 mole percent.

The vinyl polymer (C) containing at least 1 wt % of a unit with a polargroup, to be used for the invention, is a vinyl polymer containing atleast 1 wt % of a unit with a group where an element is bonded to anelement with a Pauling electronegativity difference of 0.9 (eV)^(0.9) orgreater. If the unit with the polar group is present at less than 1 wt%, it will not be possible to express sufficient adhesion with metalsheets even though the elastomer resin (B) is capsulated by the vinylpolymer (C).

As specific examples of groups with bonded elements having a Paulingelectronegativity difference of 0.9 (eV)^(0.5) or greater there may bementioned —C—O—, —C═O, —COO—, epoxy, C₂O₂, C₂O₂N—, —CN, —NH₂, —NH—, —X(X=halogen) and —SO₃—.

As examples of units with polar groups there may be mentioned vinylalcohol as an example with a —C—O— group; vinylchloromethyl ketone as anexample with a —C═O group; vinyl acids such as acrylic acid, methacrylicacid, vinyl acetate and propionic acid, and their metal salts or esterderivatives, as examples with a —COO— group; glycidyl esters ofα,β-unsaturated acids, such as glycidyl acrylate, glycidyl methacrylate,glycidyl ethamethacrylate and glycidyl itacrylate as examples with anepoxy group; maleic anhydride as an example with a C₂O₃ group; imidederivatives of maleic anhydride as examples with a C₂O₂N— group;acrylonitrile as an example with a —CN group; acrylamine as an examplewith an —NH₂ group; acrylamide as an example with an —NH— group; vinylchloride as an example with an —X group and styrenesulfonic acid as anexample with an —SO₃— group; any one or more of these may be included inthe vinyl polymer (C). The unit with the polar group contained in thevinyl polymer (C) is not limited to those mentioned above, as it issufficient to be a unit with a group to which is bonded an element witha Pauling electronegativity difference of 0.9 (eV)^(0.5) or greater.

As examples of the vinyl polymer (C) used for the invention there may bementioned simple polymers or those of two or more different types of thepolar group-containing units mentioned above, as well as copolymers ofthe aforementioned polymer group-containing units with the nonpolarvinyl monomer represented by the following general formula (b):

R₁CH=CR₂R₃  (b)

where R₁ and R₃ each independently represent an alkyl group of 1-12carbon atoms or hydrogen, and R₂ represents an alkyl group of 1-12carbon atoms, a phenyl group, or hydrogen.

As examples of the nonpolar vinyl monomer of general formula (b) theremay be mentioned aliphatic vinyl monomers including α-olefins such asethylene, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene,1-octene, 1-decene and 1-dodecene; isobutene, isobutylene, etc.; andaromatic vinyl monomers including styrene monomers, as well as alkylatedstyrenes such as o-, m-, p-methylstyrene, o-, m-, p-ethylstyrene ort-butylstyrene, addition polymer units of styrene-based monomers such asα-methylstyrene, etc.

As examples of simple polymers of polar group-containing units there maybe mentioned polyvinyl alcohol, polymethyl methacrylate and polyvinylacetate. As examples of copolymers of polymer group-containing units andnonpolar vinyl monomers there may be mentioned ethylene-methacrylic acidcopolymer, ethylene-acrylic acid copolymer, ethylene-vinyl acetatecopolymer and ionomer resins wherein the some or all of the carboxylicacid in one of these copolymers is neutralized with a metal ion,ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer,ethylene-methyl methacrylate copolymer, ethylene-ethyl methacrylatecopolymer, ethylene-glycidyl methacrylate copolymer, ethylene-maleicanhydride copolymer, butene-ethylene-glycidyl methacrylate copolymer,styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer,and styrene-maleic anhydride copolymer. From the standpoint of ensuringbarrier properties, the preferred combination is a copolymer of anα-olefin and a unit with a polar group. The vinyl polymer (C) used forthe invention may be a vinyl polymer containing at least 1 wt % of theunit with a polar group, but there is no limitation to those mentionedabove. The molecular weight of the vinyl polymer (C) is not particularlyrestricted, but it is preferably a number average molecular weight offrom 2000 to 500,000. At less than 2000 or greater than 500,000 it maynot be possible to sufficiently capsulate the elastomer resin (B).

For fine dispersion of the elastomer resin (B) capsulated by the vinylpolymer (C) in the polyester resin (A), it is important to achieve aproper balance for the interfacial tension between the vinyl polymer (C)and the polyester resin (A) and elastomer resin (B). It is preferred tocontrol the content of the polar group-containing unit so that theSpread Parameter (λ_((Resin C)/(Resin B))) of the vinyl polymer (C) withrespect to the elastomer resin (B) is positive. Ifλ_((Resin C)/(Resin B)) is positive, it is possible to ensurethermodynamic stability even with the elastomer resin (B) capsulated bythe vinyl polymer (C). The Spread Parameter between two differentpolymers is the parameter defined by S. Y. Hobbs; Polym., Vol.29, p.1598(1989) and is given by the following formula (ii):

λ_((Resin C)/(Resin B))=γ_((Resin B)/(Resin A))−γ_((Resin C)/(Resin B))−γ_((Resin C)/(Resin A))  (ii)

[where Resin A represents the polyester resin (A), Resin B representsthe elastomer resin (B) and Resin C represents the vinyl polymer (C),and γ_(i/j) is the interfacial tension between resin i and resin j,which is approximately proportional to 0.5 th power of the parameterX_(i/j) indicating the compatibility between resin i and resin j (asmaller value indicating better compatibility).]

Since the compatibility between the polyester resin (A) and theelastomer resin (B) is low and γ_((Resin B)/(Resin A))>0, the value ofλ_((Resin C)/(Resin B)) can be positive if the mixing ratio of thenonpolar vinyl monomer (Monomer V) and the polar group-containing unit(Monomer U) in the vinyl polymer (C) is adjusted so that X_(B/C), whichindicates the compatibility between the elastomer resin (B) and thevinyl polymer (C), and X_(A/C), which indicates the compatibilitybetween the polyester resin (A) and the vinyl polymer (C), as defined bythe following formulas (iii) and (iv), both approach 0:

X _(A/C) =φX _((Resin A)/(Monomer V))+(1−φ)X_((Resin A)/(Monomer U)−φ()1−φ)X _((Monomer v)/(Monomer U))  (iii)

X _(B/C) =φX _((Resin B)/(Monomer V))+(1−φ)X_((Resin B)/Monomer U))−φ(1−φ)X _((Monomer v)/(Monomer U))  (iv)

where φ represents the mixing ratio (volume ratio) of the nonpolar vinylmonomer.

Consequently, the preferred vinyl polymer (C) is determined consideringthe compatibility that will depend on the type of polyester resin (A)and the elastomer resin (B). As specific examples of preferredcombinations, when the polyester resin (A) is an aromatic polyesterresin composed of an aromatic dicarboxylic acid residue and a diolresidue and the elastomer resin (B) is a polyolefin resin, the vinylpolymer (C) is preferably a copolymer of ethylene and a unit with apolar group or SEBS having maleic anhydride or glycidyl methacrylateintroduced to at least 1 wt %; a copolymer of ethylene and a unit with apolar group will allow λ_((Resin C)/(Resin B)) to be easily controlledto a positive value by appropriately controlling the mixing ratio of theethylene and the unit with the polar group. More preferably,introduction of a functional group that has chemical action such ascovalent bonding, coordination bonding, hydrogen bonding or ion bondingwith the polyester resin (A) into a copolymer of ethylene and a unitwith a polar group can provide thermodynamic stability at the interfacebetween the polyester resin (A) and the vinyl polymer (C) uponcapsulation.

Specific copolymers of ethylene with units having polar groups includeethylene-vinyl acid copolymer, ethylene-vinyl acid ester copolymer andtheir ionomer resins, copolymers of ethylene and α,β-unsaturated acidglycidyl esters, terpolymers of ethylene, vinyl acid or vinyl acidesters and α,β-unsaturated acid glycidyl esters, and the like. Of these,ionomer resins, copolymers of ethylene and α,β-unsaturated acid glycidylesters and terpolymers of ethylene, vinyl acid or vinyl acid esters andα,β-unsaturated acid glycidyl esters are preferred. These resins exhibitrelatively strong chemical interaction with the polyester resin (A) andform stable capsulated structures with the elastomer resin (B). Mostpreferred among these from the standpoint of moldability are ionomerresins, because the strength of their chemical action with the polyesterresin (A) varies depending on the temperature.

The ionomer resins used may be any publicly known ionomer resins.Specific ones are copolymers of vinyl monomers and α,β-unsaturatedcarboxylic acids, wherein some or all of the carboxylic acid in thecopolymer is neutralized with a metal cation.

Examples of vinyl monomers include the aforementioned α-olefin andstyrene-based monomers, and as examples of α,β-unsaturated carboxylicacids there may be mentioned α,β-unsaturated carboxylic acids of 3-8carbon atoms, and specifically acrylic acid, methacrylic acid, maleicacid, itaconic acid, maleic acid monomethyl ester, maleic anhydride andmaleic acid monoethyl ester.

As examples of neutralizing metal cations there may be mentionedmonovalent or divalent metal cations such as Na⁺, K⁺, Li⁺, Zn²⁺, Mg²⁺,Ca²⁺, Co²⁺, Ni²⁺, Pb²⁺, Cu²⁺ and Mn²⁺. The remaining carboxyl groupsthat are not neutralized with the metal cation may be esterified with alower alcohol.

As specific examples of ionomer resins there may be mentioned resinsthat are copolymers of ethylene with unsaturated monocarboxylic acidssuch as acrylic acid and methacrylic acid and copolymers of ethylenewith unsaturated dicarboxylic acids such as maleic acid and itaconicacid, wherein some or all of the carboxyl groups in the copolymer areneutralized with a metal ion such as sodium, potassium, lithium, zinc,magnesium or calcium. Most preferred among these, for the purpose ofimproving compatibility between the polyester resin (A) and theelastomer resin (B), are resins that are copolymers of ethylene withacrylic acid or methacrylic acid (with 2-15 mole percent of structuralunits with carboxyl groups), wherein 30-70% of the carboxyl groups ofthe polymer are neutralized with a metal cation such as Na or Zn.

A dispersed structure for the resin composition of the invention can beformed relatively easily if the elastomer resin (B) and vinyl polymer(C) used for the invention form a core-shell type elastomer, with theelastomer resin (B) as the core and the vinyl polymer (C) as the shell.A core-shell type elastomer has a two-layer structure composed of a coreand shell, where the core is in a soft rubber state and the shell on itssurface is in a hard resin state.

As examples of core-shell type elastomers there may lo be mentionedelastomers wherein the core is composed of an acrylic-based elastomer,diene-based elastomer or silicon-based elastomer, and an acrylic-basedpolymer composed mainly of an acrylate or methacrylate is graftedthereon to form the shell. Grafting refers to graft copolymerizationbetween the core resin and the shell resin.

Specifically, the elastomer composing the core is an acrylate-basedpolymer composed of a unit obtained from a monomer with the structure ofgeneral formula (c), or a diene-based polymer or an elastomer composedmainly of dimethylsiloxane.

CH₂═CR₁—CO—O—R₂  (c)

Specific examples of structural units for the aforementionedacrylate-based polymer include alkyl acrylates, alkyl methacrylates andalkyl ethacrylates, among which are preferred those wherein R₁ ishydrogen or an alkyl group of 1-12 carbon atoms and R₂ is an alkyl groupof 1-12 carbon atoms. More specifically, there may be mentioned methylacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methylmethacrylate, ethyl methacrylate, butyl methacrylate and n-octylmethacrylate. Preferred among these from the standpoint of impartingimpact strength are ethyl acrylate, butyl acrylate, 2-hexyl acrylate,methyl methacrylate and n-octyl methacrylate. The acrylate-based polymerforming the core may be any one of these polymers alone, or copolymersof two or more thereof.

The acrylate-based polymer composing the core may also be copolymerizedwith another vinyl monomer, so long as the acrylate is the maincomponent. “Main component” means at least 50 wt %. As specific examplesof vinyl monomers there may be mentioned α-olefin monomers,styrene-based monomers and polar vinyl monomers. More specifically, asα-olefin monomers there may be mentioned ethylene, propylene, 1-butene,1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene and1-dodecene, as styrene-based monomers there may be mentioned styrenemonomer as well as alkylated styrenes such as o-, m-, p-ethylstyrene andt-butylstyrene, halogenated styrenes such as monochlorstyrene, andα-methylstyrene, etc., and as polar vinyl monomers there may bementioned acrylic acid, acrylonitrile, maleic anhydride and imidederivatives thereof, vinyl acetate, vinyl chloride and vinyl propionate.

An acrylate-based polymer composing the core is preferably partiallycrosslinked with a crosslinking agent in order to exhibit rubberelasticity. As examples of crosslinking agents there may be mentionedpolyethylenic unsaturated vinyl monomers such as divinylbenzene,butylene diacrylate, ethylene dimethacrylate, butylene dimethacrylate,trimethylolpropane trimethacrylate, triallyl cyanurate and triallylisocyanate. The amount of crosslinking agent added is no greater than 30wt %, preferably no greater than 20 wt %, and more preferably no greaterthan 5 wt %. At greater than 30 wt % it may harden and no longer exhibitrubber elasticity.

A diene-based polymer composing the core is a polymer of a diene monomeror a hydrogenated polymer thereof, and specifically there may bementioned polybutadiene and its hydrogenated polymers, or butadiene andstyrene copolymer and its hydrogenated polymers.

The molecular weight of the polymer composing the core is notparticularly restricted, but it is preferably a number average molecularweight of 2000 or greater. At less than 2000, rubber elasticity may notbe adequately exhibited. When the core is a crosslinked acrylate-basedpolymer, the molecular weight between crosslinked points is preferablyat least 2000 from the standpoint of imparting sufficient rubberelasticity.

The glass transition temperature of the polymer composing the core(measured by a differential scanning calorimeter (DSC) with atemperature elevating rate of 10° C./min) is preferably no higher than30° C., more preferably no higher than IOC, and more preferably nohigher than −10° C. If the glass transition temperature is higher than30° C., it will be difficult to exhibit rubber elasticity at roomtemperature or below.

The shell of the core-shell type elastomer will now be explained. It isimportant for the shell to be composed of an acrylate-based polymer, andthe polarity of the acrylate-based polymer can be utilized to ensureadhesion when the core-shell type elastomer contacts with the metalsheet.

The acrylate-based polymer composing the shell is a polymer comprising aunit of general formula (c). Specifically, it is a polymer of themonomers mentioned above, and it may also be copolymerized with theaforementioned vinyl monomers so long as the acrylate unit is the maincomponent. “Main component” means at least 50 wt %. When copolymerizedwith another Vinyl monomer, the composition ratio of the acrylatecomponent is preferably at least 70 wt %. At less than 70 wt % thepolarity of the acrylate unit cannot be sufficiently utilized, and theadhesion with the metal sheet will sometimes be inadequate.

Because the core-shell type elastomer has a core of a soft rubberysubstance, the resin composing the shell must be hard from the viewpointof handling. For this reason, the glass transition temperature of theacrylate-based polymer composing the shell (measured by a differentialscanning calorimeter (DSC) with a temperature elevating rate of 10°C./min) is preferably at least 30° C., and more preferably at least 50°C.

Most preferred as the acrylate-based polymer unit composing the shell ismethyl methacrylate, because it has a glass transition temperature inthe aforementioned range and its polymerization rate is easilycontrolled.

A functional group or bond group capable of reacting with the residualterminal functional group or ester bond of polyester resin (A) is alsopreferably introduced in the acrylate-based polymer composing the shellin order to ensure compatibility with the polyester resin (A). Asspecific examples of functional groups there may be mentioned epoxy,carboxyl, hydroxyl, acid anhydride or amino groups, and when the shellis grafted, a functional group may be introduced by adding a publiclyknown vinyl monomer with one of these functional groups. As examples ofbond groups there may be mentioned ester bonds, carbonate bonds andamide bonds, and when the shell is grafted a bond group may beintroduced using an initiator with one of these bonds, as disclosed inT. O. Ahn, et al.; J. Polym. Sci. Part A, Vol.31, 435(1993). Mostpreferred among these functional groups and bond groups, from thestandpoint of reactivity, are epoxy groups and aromatic-aromatic esterbonds, and for polymerization of the shell, the epoxy group and esterbond may be introduced by adding glycidyl metharcrylate or apolyacrylate azo initiator as disclosed in T. O. Ahn, et al.; J. Polym.Sci. Part A, vol.31, 435(1993).

The amount of the unit with these functional groups or bond groups to beintroduced is determined by their respective reactivities, and there areno particular restrictions so long as the acrylate unit is the maincomponent. However, for functional groups the amount of the functionalgroup-containing unit introduced is preferably no greater than 15 wt %,and more preferably no greater than 5 wt %. At greater than 15 wt % acomb-shaped polymer is produced during the kneading step, andcompatibility with the polyester resin (A) is sometimes inadequatelyimproved. For bond groups the amount of the bond group-containing unitintroduced is preferably no greater than 15 wt %. At greater than 15 wt% the bond group-containing units form domains, and compatibility withthe polyester resin (A) may not be improved.

The core-shell type elastomer preferably contains the rubber polymercore at 20 wt % or greater, preferably 50 wt % or greater, and morepreferably 80 wt % or greater. At less than 20 wt %, sufficient impactstrength may not be exhibited.

The resin composition of the invention may be produced by a publiclyknown blending method.

Specifically, it may be produced by melting and kneading the polyesterresin (A), elastomer resin (B) and vinyl polymer (C) having anappropriate interfacial tension difference, at a prescribed temperaturesuch as 200-350° C. in a publicly known type of blender, using theinterfacial tension difference to form a capsule structure.

It may also be produced by grafting the elastomer resin (B) and thevinyl polymer (C) to form a core-shell type elastomer, and then blendingwith the polyester resin (A). The core-shell type elastomer may bepolymerized by a publicly known radical polymerization process, of whichthe emulsion polymerization process described in U.S. Pat. No. 4,096,202is preferred from the standpoint of controlling the particle size of theresulting polymer to the micro level. The following may be mentioned asa specific polymerization process, but there is no limitation to thisprocess so long as the product is a core-shell type graft elastomer andthe shell is an acrylate-based polymer.

As the first stage of the polymerization, the unit monomer for the coreis used for radical polymerization. Here, the grafting agent used is apolyethylenic unsaturated monomer with multiple double bonds, added atabout 0.1-5 wt %. The multiple double bonds of the grafting agentpreferably have different reaction rates, and specific ones are allylmethacrylate and diallyl malate. As the second state of polymerizationafter polymerization of the core polymer, the monomer for the shell andan initiator are added for graft polymerization of the shell, to obtaina core-shell type elastomer.

AS specific examples of core-shell type elastomers there may bementioned MBA resins wherein the core is polybutyl acrylate and theshell is polymethyl methacrylate, MBS resins wherein the core isbutadiene-styrene copolymer and the shell is polymethyl methacrylate,and polymers wherein the core is polydimethylsiloxane and the shell ispolymethyl methacrylate; the acrylate-based core-polymerized acrylateshell polymer disclosed in U.S. Pat. No. 4,096,202 may also be used forthe invention.

The resin composition comprising the polyester resin (A) and thecore-shell type elastomer used for the invention may also include apublicly known compatibilizer added for the purpose of improvingcompatibility between the polyester resin (A) and the core-shell typeelastomer. The amount of the compatibilizer added is preferably nogreater than 15 wt %, and more preferably no greater than 5 wt %. Atgreater than 15 wt % the compatibilizer may form an independentcompatible structure, making it difficult to exhibit a sufficientcompatibility-improving effect. As specific examples of compatibilizersthere may be mentioned reactive compatibilizers and non-reactivecompatibilizers, and as reactive compatibilizers there may be mentionedpolymers that are compatible with core-shell type elastomers and haveintroduced therein functional groups or bonds that are reactive with theterminal residue functional group or bond of the polyester resin (A).More specifically, there may be mentioned random copolymerized polymersof glycidyl methacrylate and maleic anhydride with the polymer composingthe shell of the core-shell type elastomer and block and graftcopolymerized polymers of aromatic polyesters with the polymer composingthe shell. As non-reactive compatibilizers there may be mentioned blockand graft copolymers of the polyester resin (A) with the polymercomposing the shell of the core-shell type elastomer.

Blending of the resin composition of the invention may be carried out bya publicly known resin blending method such as resin kneading, solventblending or the like. As an example of a resin kneading method there maybe mentioned a method of dry blending with a tumbler/blender, Henschelmixer or v-type blender, followed by melt kneading with a single-screwor twin-screw extruder, kneader, Banbury mixer or the like. As anexample of a solvent blending method there may be mentioned a method ofdissolving the polyester resin (A), elastomer resin (B) and vinylpolymer (C) in a common solvent for each resin, followed by evaporationof the solvent or addition of a common non-solvent and recovery of theblend.

The resin composition for coating a metal sheet of the invention mayalso contain in admixture such fiber reinforcers as glass fibers, metalfibers, potassium titanate whiskers and carbon fibers, or such fillerreinforcers as talc, calcium carbonate, mica, glass flakes, milledfibers, metal flakes and metal powder, for the purpose of improving therigidity or linear expansion properties. Preferred among such fillersare glass fibers and carbon fibers, with a fiber size of 6-60 μm and afiber length of at least 30 μm. These are preferably added in an amountof 5-15 parts by weight with respect to the total weight of the resincomposition.

Depending on the purpose, the resin composition may also containappropriately added amounts of heat stabilizers, antioxidants,photostabilizers, release agents, lubricants, pigments, flameretardants, plasticizers, antistatic agents or antibacterial orantifungal agents.

The resin composition of the invention may be widely used as a coatingmaterial for metal sheets. The metal sheets are not particularlylimited, and include steel sheets for cans such as tinned sheet iron,thin tin-plated steel sheets, electrolytic chromic acid treated steelsheets (tin-free steel) and nickel-plated steel sheets, as well as othersurface treated steel sheets including hot-dip plated steel sheets suchas hot-dip zinc-plated steel sheets, hot-dip zinc-iron alloy-platedsteel sheets, hot-dip zinc-aluminum-magnesium alloy-plated steel sheets,hot-dip aluminum-silicon alloy-plated steel sheets and hot-dip lead-tinalloy-plated steel sheets; electroplated steel sheets such as zincelectroplated steel sheets, zinc-nickel electroplated steel sheets,zinc-iron electroplated steel sheets and zinc-chromium electroplatedsteel sheets; cold-rolled steel sheets and metal sheets of aluminum,copper, nickel, zinc, magnesium and the like. Such metal sheets may becoated on either or both sides. The coating film thickness for coatingof the resin composition of the invention onto a metal sheet is notparticularly limited, but is preferably 1-300 μm. At less than 1 μm thecoating may have insufficient impact strength, and at greater than 300μm there are disadvantages in terms of economy.

A publicly known method may be used for coating onto the metal sheet.Specifically, there may be mentioned (1) a method in which the resincomposition that has been pelletized after melt kneading of a resincomposition starting material is subjected to melt kneading or meltextrusion with a T-die or ring-mounted extruder to form a film and theresulting film is subjected to thermocompression bonding with the metalsheet; (2) a method in which the step of melt kneading of the resincomposition starting material and pelletizing in (1) above is omitted,and the resin composition starting material is instead directlyintroduced into a T-die mounted melt kneader to form a film and theresulting film is subjected to thermocompression bonding with the metalsheet (for methods (1) and (2), the film may be unstretched, orstretched either in one or two directions); and (3) a method in whichthe film exiting the T-die in (1) or (2) above is directly subjected tothermocompression bonding with the metal sheet without being wound up ona roll.

Because the resin composition of the invention contains the elastomerresin (B), it can exhibit sufficient impact strength even without gradedcrystallization in the film after coating. Consequently, the metal sheetmay also be coated by (4) a method in which the resin composition ismelted and coated with a bar coater or roll, (5) a method in which themetal sheet is dipped into the molten resin composition, or (6) a methodin which the resin composition is dissolved in a solvent and spraycoated, with no particular restrictions on the coating method.

The most preferred methods of coating onto the metal sheet from thestandpoint of working efficiency are the aforementioned methods (1) to(3). When coating is accomplished by method (3), the film thickness ispreferably 1-300 um for the same reasons given above. The surfaceroughness of the film is also preferably no greater than 500 nm in termsof R_(max), with measurement of an arbitrary 1 mm length of the filmsurface roughness. At greater than 500 nm, air bubbles may be entrainedduring coating by heat-press bonding.

The resin film for coating a metal sheet of the invention is a resinfilm comprising a resin composition of the invention, and even the resinfilm prior to coating may be a resin film formed after coating by one ofthe aforementioned methods (4) to (6). A publicly known lubricant suchas disclosed in Japanese Unexamined Patent Publication HEI No. 5-186613may also be added for the purpose of improving the lubrication duringthe metal sheet coating step or the metal sheet working step. Theparticle size of the lubricant is preferably no greater than 2.5 μm. Atgreater than 2.5 μm, the mechanical properties of the resin film may bereduced. The amount of lubricant added is determined based on thewindability and deep draw workability of the metal sheet, and forexample, it is preferably no greater than 0.05 wt % for monodispersesilica with a mean particle size of 2.0 μm and no greater than 0.3 wt %for titanium dioxide with a mean particle size of 0.3 μm.

For coating of the resin film of the invention onto the metal sheet,either or both sides of the metal sheet are coated using at least theaforementioned resin film for lamination of either a single layer ormultiple layers. Here, one or more resin films may be used forlamination as a single layer or multiple layers on one or both sides ofthe metal sheet, or if necessary, another publicly known resin film, forexample, a polyester film such as a PET film or polycarbonate film, apolyolefin film such as a polyethylene film, a polyamide film such as a6-nylon film, or an ionomer film or the like, or a publicly known resincomposition film, for example a crystalline or amorphous polyestercomposition film, a polyester/ionomer composition film or apolyester/polycarbonate composition film, may be coated as lamination ofa lower layer and/or upper layer. A specific lamination method, whenusing the aforementioned methods (1) to (3), is a method in which amultilayer T-die is used to produce a multilayer film of a resin film ofthe invention with another resin film or resin composition film, and themultilayer is subjected to thermocompression bonding. When using theaforementioned methods (4) to (6), the resin composition of theinvention may be coated after coating of another resin composition, orconversely, the other resin composition may be coated after coating ofthe resin composition of the invention, to laminate multiple layers.

The resin-coated metal sheet of the invention is a metal sheet coatedwith a resin film, and the coating may be on one side or both sides. Thethickness of the metal sheet is not particularly restricted, but ispreferably 0.01-5 mm. At less than 0.01 mm it is difficult to achievestrength, and at greater than 5 mm the working becomes more difficult.

The resin-coated metal sheet of the invention is one coated with a resinfilm of the invention, but if necessary a publicly known resin film mayalso be coated on the metal sheet by lamination as a lower layer and/orupper layer for the resin film of the invention. A publicly knownadhesive may also be laminated between the metal sheet and the resinfilm of the invention. As examples of adhesives there may be mentionedthe polyester resin-based aqueous dispersion disclosed in JapaneseExamined Patent Publication SHO No. 60-12233, the epoxy-based adhesivedisclosed in Japanese Examined Patent Publication SHO No. 63-13829 andthe polymers with different functional groups disclosed in JapaneseUnexamined Patent Publication SHO No. 61-149341.

A resin-coated metal container according to the invention may be formedby a publicly known working method as a resin-coated metal containercomprising a resin-coated metal sheet of the invention. As specificmethods there may be mentioned draw ironing molding, draw-redrawmolding, stretch draw molding and the like, but the molding method isnot limited to these molding methods and may be any one that gives aresin-coated metal container using a resin-coated metal sheet of theinvention.

The resin composition of the invention is a resin composition comprisingof three components, the polyester resin (A), the elastomer resin (B)and the vinvl polymer (C) containing at least 1 wt % of a unit with apolar group, and it has a structure wherein the elastomer resin (B)capsulated by the vinyl polymer (C) is finely dispersed in the polyesterresin (A). It is thus possible to improve the impact strength of thepolyester resin (A) with the elastomer resin (B), and since theelastomer resin (B) is capsulated by the vinyl polymer (C), it ispossible to improve the compatibility between the polyester resin (A)and the elastomer resin (B) and to prevent direct contact between themetal sheet and elastomer resin (B) to thus ensure adhesion between themetal sheet and the resin composition. As a result, the metal sheetcoating resin composition of the invention can be suitably used as ametal-sheet-coating material exhibiting excellent moldability, heatresistance, impact strength, chemical resistance, mechanical strength,gas barrier properties and adhesion with metals. A metal sheet coatingresin film of the invention is a film composed mainly of a resincomposition of the invention, and can therefore be suitably used as ametal sheet coating resin film having the properties described above.

A resin-coated metal sheet according to the invention is theaforementioned resin composition or resin film coating one or both sidesof a metal sheet, and it therefore exhibits excellent adhesion betweenthe resin and the metal sheet as well as corrosion resistance, impactstrength and workability, while its excellent painting and printingproperties renders it adaptable to designing; it thus has a wide rangeof uses, including uses for metal containers such as metal cans, casesfor household electrical appliances, members of metal furniture,automobile parts such as automobile outer panels, and interior andexterior materials for construction such as interior walls and doors. Inparticular, the excellent working follow-up properties for draw moldingand draw wipe molding allow formation of metal containers with anexcellent outer appearance.

Furthermore, since a resin coated metal container of the invention is ametal container prepared by shaping a resin-coated metal sheet of theinvention, it has impact strength that can withstand impact during thecutting step, canning step, transport, etc., and heat resistance thatcan withstand drying, printing, baking, etc. after canning, as well asflavor properties (flavor preservation) and a long shelf life. It cantherefore be suitably used as a container for refreshment drinks andfoods.

EXAMPLES

The present invention will now be explained in further detail by way ofthe following examples and comparative examples.

In the following examples and comparative examples, polyethyleneterephthalate (PET) [RN163, Toyobo, KK] and polybutylene terephthalate(PBT) [1401-X04, Toray, KK] were used as the polyester resin (A),ethylene-propylene rubber (EPR) [EPO7P, JSR, KK.] and ethylene-butenerubber (EBM) [EBM2041P, JSR, KK.] were used as the elastomer resin (B),ethylene-based ionomers [Himilan 1706, 1707, Mitsui DuPont, KY.] andethylene-methacrylic acid copolymer [Newcrel N1035, Mitsui DuPont, KK.]were used as the vinyl polymer with at least 1 wt % of a unit with apolar group, and polybutyl acrylate-polymethyl methacrylate copolymer(MBA) [Paraloid EXL2314, Kureha Chemicals, KK.] was used as thecore-shell type elastomer.

Examples 1-11

A V-type blender was used for dry blending of the resin mixtureproportions shown in Table 1, and melt kneading was carried out at 260°C. in a twin-screw extruder to obtain resin composition pellets. Aftercutting out an ultrathin strip from the resin composition using amicrotome, it was dyed with a ruthenium acid and the dispersion state ofthe elastomer resin (B) and vinyl polymer (C) in the polyester resin (A)was analyzed with a transmission electron microscope. As a result, inall cases, the elastomer resin (B) was almost 100% capsulated by thevinyl polymer (C), and the sphere equivalent diameter of the elastomerresin (B) was under 1 μm as shown in Table 1, allowing fine dispersionin the polyester resin (A).

TABLE 1 Resin composition Sphere Polyester Elastomer Vinyl equivalentresin resin polymer diameter Type wt % Type wt % Type wt % (μm) Example1 PET 87 EBM 10 1706 3 0.5 Example 2 PET 80 EBM 15 1706 5 0.5 Example 3PET 80 EBM 10 1706 10 0.5 Example 4 PET 80 EBM 10 1707 10 0.5 Example 5PET 80 EBM 10 N1035 10 0.5 Example 6 PET 90 EPR 5 1706 5 0.8 Example 7PET 80 EPR 10 1706 10 0.8 Example 8 PET 70 EPR 15 1706 15 0.8 Example 9PET 90 EPR 5 1707 5 0.8 Example 10 PET 80 EPR 10 1707 10 0.8 Example 11PET 70 EPR 15 1707 15 0.8

The pellets were used to obtain a 30-μm thick film with an extrusionT-die (extrusion temperature: 280° C.).

The film was laminated over both sides of 2.5-mm thick tin-free steelheated to 250° C., and then quenched by water cooling to below 100° C.within 10 seconds.

The resin-coated metal sheet thus obtained was immersed for 24 hours atroom temperature in an aqueous solution (UCC solution) containing 1.5 wt% citric acid and 1.5 wt % salt or sodium chloride, and then evaluatedby the peeled length (mm) of the film (average of 10 samples). Theevaluation scale was ⊚: 0.0 mm, ∘: 0.0-0.5 mm, Δ: 0.5-2.0 mm and X: over2.0 mm. The results of adhesion testing are shown in Table 2.

The impact strength evaluation of the resin-coated metal sheets wascarried out by the DuPont falling impact test. After dropping a 0.5 kgsteel ball on the metal sheet from a height of 30 cm, the steel sheetwas placed as a base with the protruding side (r=8 mm) of the sample onthe top and a wall was formed with a soft rubber resin around theprotruding area, 1.0% saline was poured therein, the sample was used asthe anode while the platinum set near the protruding area was used asthe cathode, and the ERV value (mA) was measured upon application of avoltage of +6 V. The ERV value was evaluated according to the scalegiven below. After then placing the resin-coated metal sheet in a 0° C.constant temperature tank for 24 hours, the same impact strengthevaluation was conducted to evaluate the low temperature impactstrength. The evaluation was made based on the following scale: ⊚: allsamples less than 0.01 mA, ∘: 1-3 samples 0.01 mA or greater, Δ: 3-6samples 0.01 mA or greater and X: 7 or more samples 0.01 mA or greater.The results are shown in Table 2.

TABLE 2 Normal temperature Low temperature Adhesion impact strengthimpact strength Example 1 ⊚ ⊚ ⊚ Example 2 ⊚ ⊚ ⊚ Example 3 ⊚ ⊚ ⊚ Example4 ⊚ ⊚ ⊚ Example 5 ⊚ ⊚ ⊚ Example 6 ⊚ ∘ ∘ Example 7 ⊚ ⊚ ⊚ Example 8 ⊚ ⊚ ⊚Example 9 ⊚ ∘ ∘ Example 10 ⊚ ⊚ ⊚ Example 11 ⊚ ⊚ ⊚

Examples 12 and 13

A V-type blender was used for dry blending of the resin mixtureproportions shown in Table 3, and melt kneading was carried out at 230°C. in a twin-screw extruder to obtain resin composition pellets. AS aresult of analysis of the dispersion state in the same manner as forExamples 1-11, it was confirmed that the elastomer resin (B) was 100%capsulated by the vinyl polymer (C), and that the sphere equivalentdiameters of the elastomer resins (B) were under 1 μm as shown in Table3, allowing fine dispersion in the polyester resin (A).

TABLE 3 Resin composition Sphere Polyester Elastomer equivalent resinresin Vinyl polymer diameter Type wt % Type wt % Type wt % (μm) Example12 PBT 80 EPR 10 1706 10 0.6 Example 13 PBT 80 EBM 10 1706 10 0.5

Films were fabricated in the same manner as for Examples 1-11 and werestretched over both sides of 2.5-mm thick tin-free steel, and theadhesion and impact strength were evaluated. The results are shown inTable 4.

TABLE 4 Normal temperature Low temperature Adhesion impact strengthimpact strength Example 12 ⊚ ⊚ ⊚ Example 13 ⊚ ⊚ ⊚

Examples 14-16

A V-type blender was used for dry blending of the resin mixtureproportions shown in Table 5, and melt kneading was carried out at 240°C. in a twin-screw extruder to obtain resin composition pellets. As aresult of analysis of the dispersion state in the same manner as forExamples 1-11, it was confirmed that core-shell type elastomers hadsphere equivalent diameters of under 1 μm as shown in Table 5, allowingfine dispersion in the polyester resin (A).

TABLE 5 Resin composition Sphere Core-shell type equivalent Polyesterresin elastomer diameter Type wt % Type wt % (μm) Example 14 PET 90 MBA10 0.25 Example 15 PET 80 MBA 20 0.25 Example 16 PET 70 MBA 30 0.25

Films were fabricated in the same manner as for Examples 1-11 (but withan extrusion temperature of 240° C.) and were stretched over both sidesof 2.5-mm thick tin-free steel, and the adhesion and impact strengthwere evaluated. The results are shown in Table 6.

TABLE 6 Normal temperature Low temperature Adhesion impact strengthimpact strength Example 14 ⊚ ⊚ ⊚ Example 15 ⊚ ⊚ ⊚ Example 16 ⊚ ⊚ ⊚

Comparative Example 1

Based on the examples of Japanese Examined Patent Publication HEI No.2-9935, a twin-screw extruded film comprising two layers, PBT and PET(PBT layer: 10 μm, PET layer: 20 μm, refractive index in direction ofPET layer film thickness: 1.526) was laminated onto tin-free steel underthe same conditions as Examples 1-11 (coated with the PBT layer adheredto the tin-free steel), and the adhesion and impact strength wereevaluated in the same manner as in Examples 1-11.

Comparative Example 2

Based on the examples of Japanese Unexamined Patent Publication HEI No.2-57339, a twin-screw extruded polyester film (a film composed of aterephthalic acid/isophthalic acid/ethylene glycol residue (78/22/100),specific gravity: 1.3387, thickness: 30 μm, surface orientationcoefficient: 0.120) was laminated onto tin-free steel under the sameconditions as Examples 1-11, and the adhesion and impact strength wereevaluated in the same manner as in Examples 1-11.

Comparative Example 3

Based on Example 1 in Japanese Unexamined Patent Publication SHO No.64-22530, a 108 μm unstretched PET film was heat treated afterstretching at 95° C. to a factor of 2.7 in the lengthwise direction andat 105° C. to a factor of 2.6 in the widthwise direction, to obtain anapproximately 20 μm stretched film. The film was laminated onto tin-freesteel under the same conditions as Examples 1-11, and the adhesion andimpact strength were evaluated in the same manner as in Examples 1-11.

Comparative Example 4

Based on Example 1 in Japanese Unexamined Patent Publication HEI No.7-195617, PET and an ionomer (Himilan 1707) were melt kneaded at aweight ratio of 90/10 to obtain pellets. The pellets were used tofabricate a film in the same manner as Examples 1-11, and this wasstretched over both sides of 2.5-mm thick tin-free steel and theadhesion and impact strength were evaluated.

Comparative Example 5

Based on Example 1 in Japanese Unexamined Patent Publication HEI No.7-290643, PET, an ionomer (Himilan 1707) and a polyester elastomer(Haitoreru 4057, Toray-DuPont, KK.) were melt kneaded at a weight ratioof 80/10/10 to obtain pellets. The pellets were used to fabricate a filmin the same manner as Examples 1-11, and this was stretched over bothsides of 2.5-mm thick tin-free steel and the adhesion and impactstrength were evaluated.

The results for Comparative Examples 1-5 are shown in Table 7.

TABLE 7 Normal temperature Low temperature Adhesion impact strengthimpact strength Comp. Ex. 1 ∘ ∘ Δ Comp. Ex. 2 ∘ x x Comp. Ex. 3 Δ Δ ΔComp. Ex. 4 ⊚ Δ x Comp. Ex. 5 ⊚ ∘ Δ

Examples 17-21, Comparative Examples 6-10

The resin-coated metal sheets obtained in Examples 1, 7, 14-16 andComparative Examples 1-5 were cut into disks with a 150 mm diameter andsubjected to deep draw working in 4 stages using a drawing die andpunch, and from each there were fabricated 10 seamless side containerswith a 55 mm diameter (hereunder referred to as “cans”).

The cans were evaluated and tested, and the results of evaluation basedon the following scales are shown in Table 8.

(1) Deep Draw Workability I (Evaluation of Film Surface Layer)

∘: All 10 cans had satisfactorily worked films with no whitening orfracture in the films on the inside or outside of the cans.

Δ: 1-5 cans had whitening of the film at the can tops.

X: At least 6 cans had film fracture in part of the films.

(2) Deep Draw Workability II (Evaluation of Can Interior Film)

∘: All 10 cans had satisfactorily worked inner and outer sides and gavea value of 0.1 mA or lower in a rust proof test on the can interior filmside (current value (ERV value) (mA) upon application of a voltage of +6V in 1.0% saline, using the can as the anode and platinum as thecathode).

X: At least 3 cans exceeded 0.1 mA in a rust proof test on he caninterior film side.

(3) Impact Strength

Satisfactorily deep draw worked cans were filled with water, and afterdropping 10 cans for each sample from a height of 10 cm onto a vinylchloride tile floor, an ERV test was conducted in the cans.

∘: All 10 cans 0.1 mA or lower.

Δ: 1-5 cans exceeded 0.1 mA.

X: At least 6 cans exceeded 0.1 mA.

(4) Heat Resistant Brittleness

Satisfactorily deep draw worked cans were heated at 200° C.×5 minutes,and then the impact strength was measured by the method described aboveto evaluate the heat resistant brittleness.

TABLE 8 Heat Deep draw Deep draw Impact resistant workability Iworkability II strength brittleness Example 17 ∘ ∘ ∘ ∘ Example 18 ∘ ∘ ∘∘ Example 19 ∘ ∘ ∘ ∘ Example 20 ∘ ∘ ∘ ∘ Example 21 ∘ ∘ ∘ ∘ Comp. Ex. 6 Δx — — Comp. Ex. 7 ∘ ∘ Δ x Comp. Ex. 8 ∘ x Δ Δ Comp. Ex. 9 ∘ ∘ Δ x Comp.Ex. 10 ∘ ∘ ∘ Δ

According to these results, the resin compositions of the inventiondemonstrated more excellent adhesion with metal sheets and impactstrength, and particularly impact strength at low temperature, comparedto the comparative examples. Furthermore, the resin-coated metal sheetsof the invention also demonstrated excellent film working follow-upproperties, and the resin-coated metal containers of the inventiondemonstrated excellent impact strength and heat resistant brittleness.

Industrial Applicability

The resin composition of the invention maintains the heat resistance,workability, adhesion with metal sheets, gas barrier properties andflavor properties of the polyester resin (A), while the elastomer resin(B) further enhances the elongation and impact strength of the polyesterresin (A) and the vinyl polymer (C) capsulates the elastomer resin (B)to improve the compatibility between the polyester resin (A) and theelastomer resin (B); in addition, direct contact between the metal sheetand the elastomer resin (B) is prevented to ensure adhesion between themetal sheet and the resin composition. This results in excellentproperties including moldability, heat resistance, impact strength,chemical resistance, mechanical strength, gas barrier properties andadhesion with metals, which render it suitable for use as a coatingmaterial for metal sheets.

Moreover, metal-sheet-coating resin films, resin-coated metal sheets andresin-coated metal containers according to the invention, which employthe resin composition of the invention, can be suitably used for variousmetal sheet coating materials, various metal members such as containers,and metal containers with excellent storing and flavor properties.

Because the resin-coated metal sheets of the invention have their metalsheet surfaces precoated with the resin, it is possible to eliminate thepainting steps for customers and thus provide an effect that cancontribute to a simpler process and reduced costs for customers.

What is claimed is:
 1. A resin film-laminated metal sheet comprising aresin layer laminated on a metal sheet, said resin laminated layercomprising a polyester resin (A) having an intrinsic viscosity of0.5-2.0 dl/g, an elastomer resin (B) and a vinyl polymer (C) containingat least 1 wt % of a unit with a polar group, wherein said threecomponents (A), (B) and (C) are melt-mixed to have a structure whereinthe elastomer resin (B) is finely dispersed in the polyester resin (A)and at least a portion of the elastomer resin (B) is capsulated by thevinyl polymer (C), wherein the elastomer resin (B) is softer than thevinyl polymer (C).
 2. A resin film-laminated metal sheet comprising aresin layer laminated on a metal sheet, said resin laminated layercomprising a polyester resin (A) having an intrinsic viscosity of0.5-2.0 dl/g, an elastomer resin (B) and a vinyl polymer (C) containingat least 1 wt % of a unit with ethylene and a polar group, and having astructure wherein the elastomer resin (B) is finely dispersed in thepolyester resin (A) and at least a portion of the elastomer resin (B) iscapsulated by the vinyl polymer (C), wherein the elastomer resin (B) issofter than the vinyl polymer (C).
 3. A resin film-laminated metal sheetcomprising a resin layer laminated on a metal sheet, said resinlaminated layer comprising a polyester resin (A) having an intrinsicviscosity of 0.5-2.0 dl/g, and a core/shell type elastomer resincomprising a core of an elastomer resin (B) and a shell of a vinylpolymer (C) comprising an acrylate-based polymer and an epoxy group oran aromatic polyester bond is introduced into the acrylate-based polymerat up to 15 wt % with respect to acrylate units, and having a structurewherein the core/shell type elastomer resin is finely dispersed in thepolyester resin (A), wherein the elastomer resin (B) is softer than thevinyl polymer (C).
 4. A resin film-laminated metal sheet comprising aresin layer laminated on a metal sheet, said resin laminated layercomprising a crystalline polyester resin (A) having an intrinsicviscosity of 0.5-2.0 dl/g, an elastomer resin (B) and a vinyl polymer(C) containing at least 1 wt % of a unit with a polar group, and havinga structure wherein the elastomer resin (B) is finely dispersed in thepolyester resin (A) and at least a portion of the elastomer resin (B) iscapsulated by the vinyl polymer (C), wherein the elastomer resin (B) issofter than the vinyl polymer (C).
 5. A resin film-laminated metal sheetcomprising a resin layer laminated on a metal sheet according to any oneof claims 1-4, wherein the sphere equivalent diameter of the elastomerresin (B) finely dispersed in the polyester resin (A) is no greater than1 μm.
 6. A resin film-laminated metal sheet comprising a resin layerlaminated on a metal sheet according to any one of claims 1-4, whereinthe resin layer comprises 1-50 parts by weight of the elastomer resin(B) and 1-50 parts by weight of the vinyl polymer (C) with respect to100 parts by weight of the polyester resin (A).
 7. A resinfilm-laminated metal sheet comprising a resin layer laminated on a metalsheet according to any one of claims 1-4, wherein the polyester resin(A) is composed of an acid component comprising 50-95 mole percent ofterephthalic acid and 50-5 mole percent of isophthalic acid and/ororthophthalic acid, and a diol component comprising a glycol of 2-5carbon atoms.
 8. A resin film-laminated metal sheet comprising a resinlayer laminated on a metal sheet according to any one of claims 1-4,wherein the elastomer resin (B) is a polyolefin resin.
 9. A resinfilm-laminated metal sheet comprising a resin layer laminated on a metalsheet according to claim 8, wherein the polyolefin resin is a copolymerof ethylene and an α-olefin of 3 or more carbon atoms, or a terpolymercomprising ethylene, an α-olefin of 3 or more carbon atoms and anon-conjugated diene.
 10. A resin film-laminated metal sheet comprisinga resin layer laminated on a metal sheet according to any one of claims1-4, wherein the vinyl polymer (C) is an ionomer resin.
 11. A resinfilm-laminated metal sheet comprising a resin layer laminated on a metalsheet according to any one of claims 1, 2 or 4, wherein the elastomerresin (B) and vinyl polymer (C) form a core-shell type elastomer, withthe elastomer resin (B) as the core and the vinyl polymer (C) as theshell.
 12. A resin film-laminated metal sheet comprising a resin layerlaminated on a metal sheet according to claim 11, wherein the vinylpolymer (C) is an acrylate-based polymer.
 13. A resin film-laminatedmetal sheet comprising a resin layer laminated on a metal sheetaccording to claim 12, wherein units containing epoxy groups or aromaticpolyester bonds are introduced into the acrylate-based polymer at nogreater than 15 wt % with respect to the acrylate units.
 14. A resinfilm-laminated metal sheet comprising a resin layer laminated on a metalsheet according to any one of claims 1-4, wherein said resin compositioncontains a pigment.
 15. A resin film-laminated metal container made by aprocess comprising at least one of stretching, ironing and drawing ofthe resin film-laminated metal sheet according to any one of claims 1-4.16. A resin film-laminated metal container made by a process comprisingat least one of stretching, ironing and drawing of the resinfilm-laminated metal sheet according to claim
 5. 17. A resinfilm-laminated metal container made by a process comprising at least oneof stretching, ironing and drawing of the resin film-laminated metalsheet according to claim
 6. 18. A resin film-laminated metal containermade by a process comprising at least one of stretching, ironing anddrawing of the resin film-laminated metal sheet according to claim 7.19. A resin film-laminated metal container made by a process comprisingat least one of stretching, ironing and drawing of theresin-film-laminated metal sheet according to claim
 8. 20. A resinfilm-laminated metal container made by a process comprising at least oneof stretching, ironing and drawing of the resin film-laminated metalsheet according to claim
 9. 21. A resin film-laminated metal containermade by a process comprising at least one of stretching, ironing anddrawing of the resin film-laminated metal sheet according to claim 10.22. A resin film-laminated metal container made by a process comprisingat least one of stretching, ironing and drawing of the resinfilm-laminated metal sheet according to claim
 4. 23. A resinfilm-laminated metal container made by a process comprising at least oneof stretching, ironing and drawing of the resin film-laminated metalsheet according to claim
 12. 24. A resin film-laminated metal containermade by a process comprising at least one of stretching, ironing anddrawing of the resin film-laminated metal sheet according to claim 13.25. A resin film-laminated metal container according to claim 15,wherein said process comprises ironing or deep drawing.
 26. A beveragecan made of a resin film-laminated metal sheet according to claim
 1. 27.A beverage can made of a resin film-laminated metal sheet according toclaim
 2. 28. A beverage can made of a resin film-laminated metal sheetaccording to claim
 3. 29. A beverage can made of a resin film-laminatedmetal sheet according to claim
 4. 30. A resin film-laminated metal sheetcomprising a resin layer laminated on a metal sheet according to any oneof claims 1-4, wherein the elastomer resin (B) has a glass transitiontemperature of no higher than 30° C. and the vinyl polymer (C) has aglass transition temperature of at least 30° C.